This invention relates to a sailboat having a multiple hull structure, and including fixed airfoils for improved performance particularly when sailing into the wind.
All sailboats suffer from the problem that the wind is variable and not subject to control. This problem can be a serious one, when it is considered that the forces generated by the wind vary with the square of the wind velocity. For example, a 30-knot wind exerts nine times the force of a 10-knot wind.
For thousands of years sailors have responded to this problem by carrying larger or more sails in light winds, and fewer or smaller sails in strong winds. An alternative to the technique of changing sails in the technique of reefing, that is the gathering up of a portion of the sail and securing it against a spar. Although reefing makes it possible for a boat to survive and to make controlled maneuvers in high wind, its ability to sail to windward is reduced as the sail area is reduced. A boat that can sail with full sail in any direction within a 270.degree. arc, may be limited to a 180.degree. or less when the sail is triple reefed, or reduced by two-thirds. Under such conditions, a boat could be wrecked on a lee shore while under perfect control.
The reason for the reduction in the ability of a boat to sail into the wind when the sail is reefed, is the reduction in the overall efficiency of all of the rigging exposed to the wind. The sail itself may be highly efficient, with a lift-to-drag ratio of 10 corresponding to a drag angle of 6.degree.. However, all of the standing rigging including mast, stays, shrouds and spreaders have lift-to-drag ratios of zero for a drag angle of 90.degree.. The boat, as a whole, responds to the net combined drag angle of all of the parts exposed to the wind. With the full sail aloft, the net combined drag angle may be as low as 15.degree. or 20.degree.; and this would allow the boat to sail within 40.degree. or 45.degree. of the eye of the wind. As the sail area is reduced (the component of the rigging with the desirable drag angle), the combined drag angle of all of the rigging increases. With no sail aloft, the overall drag angle is 90.degree.; and in this condition the courses available to the boat are restricted to generally downwind and perhaps 45.degree. to either side of downwind.
Assuming for purposes of discussion that the mast and all other rigging are cylindrical. A cylinder, and therefore all of these rigging components, have a lift-to-drag of zero and a drag angle of 90.degree.. The drag for a cylindrical member is roughly proportional to the diameter. On a medium size sailboat, the mast might be 6 inches in diameter and the rest of the rigging about 1/4 inch wires. The mast, then, is responsible for more drag than all of the other standing rigging combined.
An object of this invention is to provide an improved sailboat which will sail more efficiently in both light winds and strong winds.
Another object of this invention is to provide an improved sailboat having both fixed and flexible sails, wherein the boat is able to beat to windward on either tack without the benefit of the flexible sail.
A further object of this invention is to provide an improved sailboat wherein a heavy rigging spar is formed as an airfoil to reduce drag and provide lift, thereby improving substantially the lift-to-drag ratio of the boat frame and rigging.
Still another object of this invention is to provide an improved sailboat wherein the exposed spars are configured as airfoils to reduce drag and provide lift to enable the sailing of the boat without the flexible sail, and wherein the presented sail area of the flexible sail may be changed readily from 0 to 100 percent.
These objects are accomplished in a sailboat having the following structural features. A tripod boat frame is supported on the water by three independent buoyant hulls. The tripod frame includes three spars extending outwardly and downwardly from a center juncture point, and provides hull support points at the respective distal ends of these spars. These frame spars include a windward spar providing a windward support point and two leeward spars providing two leeward support points. A mast spar is mounted on the frame at the center juncture point, with its masthead disposed equidistant from the leeward support points and toward the windward support point. The three independent buoyant hulls are coupled to the three frame support points. An independent direction control and steering means is provided for each of the three hulls. The mast spar is configured, at least in part, as an airfoil symmetrical about its longitudinal axis with both edges as leading edges, and with the chord of the airfoil being fixed in a plane parallel with a line between said leeward support points.
More particularly, the leeward spars are each configured, at least in part, as an airfoil symmetrical about its longitudinal axis with both edges as leading edges, with the chord of the airfoil being fixed in a plane parallel with a line between the leeward support points.
Still more particularly a sail is mounted on the sailboat for disposition generally in a plane defined by the two leeward support points and the masthead, whereby the sail is inclined from the leeward support points toward the windward support point.
Still more particularly, the sail has its foot attached to a roller boom extending between the leeward support points, whereby the sail may be reefed by rolling onto the boom to present 0 percent to 100 percent sail area to the wind.
The novel features and the advantages of the invention, as well as additional objects thereof, will be understood more fully from the following description when read in connection with the accompanying drawings.